Aluminium bearing alloy finds its application in sliding or plain bearing of an internal combustion engine, but there is an increasing demand on improving the seizure resistance and fatigue strength thereof recently as higher load and temperature requirements are imposed upon the plain bearing with an increase in the speed of operation and the output of such engine. An improvement in the seizure resistance or fatigue strength requires an improved surface characteristics of the plain bearing, for which the use of a low melting metal, such as Sn, Pb, Bi or the like, for example, is essential.
The use of Sn as a low melting point metal in an aluminium bearing alloy is known in the prior art, as exemplified by Japanese Patent Publication No. 14,990/1989, and another aluminium bearing alloy using Bi as a low melting point metal is also known (see Japanese Laid-Open Patent Application No. 235,436/1987).
Generally, the use of a low melting point metal contributes to improving the seizure resistance and fatigue strength, but if the amount of low melting metal used is excessive, its grains are too large, or a melting point is too low with respect to an environment in which the bearing is to be used, there is an adverse effect in that the fatigue is likely to occur. By way of example, Bi has a higher melting point than Sn, and is effective generally in achieving a higher melting point for Al matrix, but this is influenced by the kind of other elements added as well as the amount of such addition, with consequence that a simple addition of Bi cannot assure an excellent seizure resistance or fatigue strength.